During a growing period of corn, etc., a triazine-based herbicide such as atrazine and acid anilide-based herbicides such as alachlor and metolachlor have been conventionally used, while atrazine shows low efficacy to gramineous weeds, and arachlor and metolachlor show low efficacy to broad-leaved weeds. It is therefore difficult at present to control gramineous weeds and broad-leaved weeds at the same time with a single herbicide. Further, the above herbicides are undesirable in view of an environmental problem due to their high dosage requirement.
On the other hand, it is known that specific 4-benzoyl-pyrazole derivatives have herbicidal activity (see JP-A-65-122672, JP-A-63-122673, JP-A-63-170365, JP-A-1-52759, JP-A-2-173 and JP-A-2-288866). Further, for example, pyrazolate of the following formula is known as a commercial herbicide. ##STR3##
However, pyrazole derivatives having a thiochroman ring such as compounds of the present invention have not yet been known so far.
Further, the commercially available herbicide, pyrazolate, is for use in a paddy field, and it hardly has herbicidal activity when used in a plowed field. Further, 4-benzoyl-pyrazole derivatives that have been already disclosed are insufficient in practical use although they have herbicidal activity in a plowed field. For example, the 4-benzoyl-pyrazole derivatives disclosed in JP-A-63-122672 have activity to broad-leaved weeds such as cocklebur, velvetleaf, slender amaranth, etc., when used for foliar treatment, while the activity thereof is practically insufficient. Further, they show very poor activity to gramineous weeds such as green foxtail, large crabgrass, barnyardgrass, etc. In soil treatment, the above derivatives show activity to gramineous weeds such as green foxtail, large crabgrass, barnyardgrass, etc., while they show very poor activity to broad-leaved weeds such as cocklebur, velvetleaf, slender amaranth, etc.